Hello, I would like to create some 2 part molds and noticed that the Boolean function seems to work differently if the subtracted mesh is fully enclosed in the surrounding mesh.
When part of the subtracting or “hidden” object sticks out - the cavity is created as expected and the result is only 1 mesh remaining.
When I fully inclose a object in another (for example a cube) and then use the boolean function the two objects are grouped and there does not seem to be any cavity left afterwards (eg I do a trim to “look” inside.
How can I use the boolean function so only 1 mesh is left so there is a cavity fully inside the surrounding object. For example if I fully surround a sphere with a cube use boolean with the sphere “hidden” it seems to group the two objects together and does not subtract the sphere mesh from the cube.
Hope someone can point me in the right direction on this as it’s quite important for fully include 2 part mold making.
Nevermind, I figured it out. I was hitting the “Boolean” button after hitting the Boolean icon which works great when the “hidden” object sticks out from the surrounding object.
The solution was to hit the “Voxel Merge” instead which apparently treats Objects within objects differently and successfully creates a cavity in the surrounding object successfully.
Does anyone know if there are any other differences to these two options in Boolean operation.
I’m not sure what you’re doing, but Boolean to make a cavity works like this:
Select object(s) that are hidden
Select object(s) that are visible
Pressing Boolean will delete the hidden object(s) from the visible object(s).
Here’s a gif showing it. The box outside is semi-transparent so you can see the sphere inside. Then showing it cut at the end so you can see the cavity.
Boolean will keep sharp edges/corners and the topology of the objects much better. Voxel works, but edges/corners aren’t as sharp and the topology is lost.
Thanks for your reply. When I do the same thing the two objects don’t become one when Boolean is selected. They can be “Separated”. When one sticks out they actually become one object. Only when I voxel the two objects become one when one is fully inside the other.
I do see the cavity but the objects are still separated. Is there anyway for the 2 objects to become one or is there a setting someone that I have on or off that would cause this?
Sorry, I mean to say the two objects are JOINED when boolean is pressed with the ability to “Separate” and this does not happen when the sphere is not fully enclosed.
When you want to cut an object using Boolean operations from a mold that consists of two or more parts, don’t join the mold parts and perform the Boolean operation all at once. As soon as object surfaces touch, the Boolean operation merges them, which leads to incorrect results.
Your approach of cutting a hole into the mesh and then using Voxel Remesh is not necessarily effective. As mentioned before, you need to perform the Boolean operation separately for each mold and for each individual mold part. If you apply the Boolean operation to each part individually, it will work correctly.
Roger, Here is a video of what I get when using the boolean for 1) when one object is fully enclosed in another and 2) when the inside object sticks out from the outer object. For the 1st one it looks like it just joins them together and the objects can be separated (I can see two child objects under a parent one) but in the 2nd boolean operation (I undo a few steps to get the 2 primities back) the boolean operation removes the hidden mesh completely leaving only 1 object.
Holger, That video you linked here was the one I studied before trying it myself. I thought that doing a boolean first before splitting the outer object would still work and got mystified why it wouldn’t (which is why I posted this question). It might be a good solution to split the outer object first then boolean each half separately but I just thought doing the boolean first on 2 objects is more logical as I might want a 3 or 4 part mold in the future which would complicate everything and more steps etc.
Anyway, just curious why I get joined objects with fully enclosed objects and only 1 mesh when the “hidden” object sticks out a bit.
I think the Boolean operation is actually working correctly. The issue is that the sphere mesh inside the cube has no connection to the outer mesh. That’s why you can still separate the meshes afterward.
However, as soon as you split the mesh or create a hole after the boolean operation, Separate should no longer work, because then the meshes are connected. The Boolean operation itself should still work regardless.
Also, when recording your videos, it would be better to enable X-Ray mode—for both meshes. That way, you can clearly see what’s happening during the Boolean operation and whether it’s working or not. This is much clearer than switching the material to transparent.
Thanks Holger, that makes so much sense now. The boolean only works when faces of both objects are intersecting and this doesn’t happen when 1 object is fully enclosed. At least I know the reason now and the solution is to split the outer object first.
This is incorrect. It works without the faces of the inner object touching. The object fully enclosed, when Booleaned, will leave a cavity in the external object.
It works both ways. But an object touching another when using the Boolean function, creates a connection between the two objects meshes and makes it so they cannot be separated.
Maybe the source of confusion is not how Boolean works but rather what separate does.
Separate simply visits every faces of the objects that are “connected” together. Each connected patch will result in a separate object.
